As a director Lucy Bailey is clearly at home in ancient Rome: she gave us a blackly sardonic Titus Andronicus at Shakespeare's Globe; now she comes up with a visceral RSC Julius Caesar that certainly captures the chaos of a divided city. What emerges rather less clearly is the play's subtle characterisation and sophisticated political debate.

From the start, when we see Romulus and Remus noisily scrapping like Japanese wrestlers under a towering she-wolf, Bailey's thesis is clear: that Rome is a city founded on violence. The assassination of Caesar, as recorded in Suetonius, is a prolonged, messy fight to the death, and is ironically echoed, on the plebeian level, by the vicious street murder of Cinna the poet. Exhalations whizz in the night air which is filled with ominous thunder. And William Dudley's video designs evoke the muscular momentum of Muybridge photographs by projecting epic images of multiplying figures onto six pivoting screens. For once, Rome doesn't seem drastically underpopulated.

But this is also a play that poses a difficult question: at what point, if any, is political murder justified? And here Bailey's attitude seems uncertain. Greg Hicks' Caesar is implacably arrogant, thrusting a petitioner venomously aside as he cries "I spurn thee like a cur", but nothing suggests he is a dangerous tyrant.

On the other side of the equation, Bailey never fully explores the monstrous intellectual vanity of Brutus. Sam Troughton plays him perfectly well as a muddled liberal in a world of realpolitik. What one misses is the fatal self-regard of a man who is wrong about every single tactical decision, and the double-think of an assassin who says of Caesar, "Let's carve him as a dish fit for the gods." In other words, murder is fine as long as it's aesthetically executed.

This reluctance to delve too far below the surface applies to most of the main characters. John Mackay's Cassius is a nervy hysteric propelled by envy: his best moment comes late on when, knowing Brutus is wrong about the battle-plans, he stoically accepts his fate. Darrell D'Silva's Mark Antony is also more of a beefy playboy, throwing up after a night's boozing, than a silky master of political rhetoric.

There is nothing radically wrong with any of these performances. But one feels much of the energy has gone into the impressive physical staging, rather than into an analysis of a complex, subversive play about the morality of the supposedly necessary murder.